You can almost certainly fabricate a better fairing for the camper shell, which most likely has a flat front. Can you post a picture of it or something similar? Is it one of these?
If so, those are very heavy and will certainly make your truck into a fuel pig. You might want to reconsider and trade it in on a travel trailer instead, so you can park your home and drive your truck without it.
Your Ram 2500 probably is equipped with Load Range E tires, which are good for 80psi. My empty GMC 1500 rides and handles well at 80 psi all around, your truck with a heavy camper on the bed probably needs those 80psi just for safety. Pump up those tires to whatever the sidewall says for maximum.
I'm surprised to hear you gained 2mpg with just a K&N filter. It made zero difference on my 1997 Grand Am, and I've never read a report of one actually helping. I suspect your old filter was clogged, or Dodge's engineers really failed badly when they designed that system with such a cheap-to-fix bottleneck (which, from their point of view, merely requires a different size/shape filter).